Amount advanced not repaid since August 2018

Hello, I would like some advice from you. My travel agent, whom I have always trusted and who has always done an impeccable job, owes me since August 2000 euros. He was supposed to pay me back in September, then in January, but nothing happens. We exchanged dozens of messages, I threatened him, I contacted his boss. But finally without results except for promises that he does not keep. I think I will take the next step, i.e. contact either a lawyer or a private investigator in Delhi to handle this case. I have an acknowledgement of debt from him and I have kept all the exchanges I had with him on this subject.